Plasma kiln

ABSTRACT

A plasma kiln with a horizontal cristallizer moved within reach of a plasma torch, provided with parallel supply conductors of electric current to both ends of the cristallizer and with observation means of the cristallizer connected to the supply of the working gas of the plasma torch.

219-1z1. 12-18-73 XR 31,780,201

United States Patent 91 Dembovskj [451 Dec. 18, 1973 PLASMA KILN [75] Inventor: Vladimir Dembovsk,0strava,

Czechoslovakia [73] Assignee: Vysoka Skola Banska Ostrava [22] Filed: Feb. 6, 1973 [21] Appl. N0.: 330,025

[52] US. Cl. 13/31, 13/1, 219/121 P [51] Int. Cl. H05b 7/00 [58] Field ofSearch 13/1,31;219/121 P,

219/121 BB, 121 A [56] References Cited UNITED STATES PATENTS.

Kurtz et a1. 219/121 EB Chopra et a1. Brzozowski et al....

Primary Examiner-Roy N. Envall, Jr AIt0rneyArthur O. Klein 5 7 ABSTRACT A plasma kiln with a horizontal cristallizer moved within reach of a plasma torch, provided with parallel supply conductors of electric current to both ends of the cristallizer and with observation means of the cristallizer connected to the supply of the working gas of the plasma torch.

4 Claims, 3 Drawing Figures PLASMA KILN BACKGROUND OF THE INVENTION The invention relates to a plasma kiln for melting of metals and for making of ingots, using a horizontal cristallizer.

Known plasma kilns for melting of metals and for making of ingots operate on a number of different principles. One of these processes, based on the principle of electric arc kilns provided with a ceramic lining, uses for closing the circuit between the plasma torch and the molten metal a special electrode. Another process uses a plasma torch above a vertical cristallizer, into which the metal is gradually cast and where it solidifies to the shape of an ingot. There is also a known process, where the metal passes trough a plasma torch and only thereafter grows in the plasma kiln to the shape of an ingot. This process of melting metals in a vertical cristallizer secures a minimum contamination of the metal from the melting vessel and prevents also any possibility of contamination and gasification in the course of casting, but losses of heat energy by transmission to the walls of the cristallizer make impossible to melt larger amounts of metals with high melting point and thus obtain a perfectly and wholly homogeneous product. The homogenity is improved when using for melting a vertical cristallizer by adjusting the charge to fusing electrodes, to tablets or presslings of prior homogenized waste. None of the actually known plasma kilns allows to obtain a high purity of the remolten metal without inclusion and simultaneously a high degree of homogenity. The observation means arranged in the working space of plasma kilns for controlling the process of melting metals are contaminated by the evaporated metal and become inoperative. Protection of these observation means is at present secured by stable or rotating screens and in some cases also by the possibility of exchange of special protective glasses.

The supply of the electric current to the molten metal in metal cristallizers of plasma kilns is actually arranged so that one pole of an electric direct current is connected to the cristallizer below the nozzle of the used plasma torch. If the supply of the electric current for a horizontal cristallizer is beyond the longitudinal axis of the nozzle of the plasma torch, the flow of the plasma is not symmetrical and a deviation thereof is caused by the generated electromagnetic field. It is in such cases necessary to change constantly the connection place of electric current, what is due to the high intensities of these currents for instance by contact means rather difficult to realize. A not symmetric flow of the plasma causes a reduction of concentration of the heat energy and frequently prevents the technologically required control of solidifying of metal in the cristallizer.

SUMMARY OF THE INVENTION It is an object of this invention to provide a plasma kiln for the above mentioned purposes with a horizontal cristallizer, where the melting of the metal could be efficiently controlled. The plasma kiln according to this invention comprises a horizontal cristallizer in the shape of a trough limited in the longitudinal direction by face walls and situated inside a melting space of a plasma kiln, the cristallizer being within reach of the melting effect of a plasma torch and adapted to be moved in direction of its longitudinal axis, the plasma kiln provided furthermore with observation means con nected to the supply of working gas of the plasma torch creating an overpressure in this region with respect to the kiln space and diverting any evaporated gas from the observation means. The cristallizer has advantageously the shape of a trough with water cooled walls and its ends are connected by a couple of parallel branches of conductors to the source of electric current. Adjustable resistor may be provided in one or both parallel branches of these conductors.

The cristallizer of the kiln according to this invention operates on the principle of melting zones and enables a continuous melting and solidifying of metals. The horizontal cristallizer fulfills in this case the task of a melting vessel and of an ingot mould. Due to the application of a horizontal cristallizer it is possible to remelt metals in powder shape, or scrap pieces, fractions of electrolytically refined metal pieces and similar without required prior special treatment of this material. The horizontal cristallizer, having a double wall, determining a space for passage of water for cooling its walls is suitable for remelting of metal of powder consistence and for zone refining. A cristallizer composed of parallel tubes through which the cooling water is passing, is particularly suitable for remelting and melting of piece material having a high melting point. In the course of melting in such a cristallizer the metal is in contact with a part of the surface of the tubes only, which form the melting trough, so that a perfect melting of the ingot up to its surface is secured. In that case no high losses of heat energy are experienced due to a small contact surface of the ingot and the cristallizer. The working gas supplied to the space of the observation means in a small amount secures a direction of streaming from the glass of the observation means towards the kiln space and thus also a removal of the evaporated material that could cause a contamination of the observation glass, whereby the overall simplicity of the observation means isis maintained. The interconnection of the supply of the working gas to the observation means of the kiln with the gas supply to the plasma torch secures a continuous overpressure of gas in the observation means with respect to the kiln space. The effect of the connection of the electric supply conductors according to this invention is that stable connections of electric current to both ends of the horizontal cristallizer by a couple of parallel branches of electric conductors secure the flow of the plasma in direction of the longitudinal axis of the nozzle of the plasma torch in the course of movement of the cristallizer from one extreme position to the other one without changing the place of supply of electric current. By application of parallel supply branches of electric current with adjustable resistors, the direction of flow of the plasma from the nozzle can be controlled and thus the melting process when treating piece, clump or powder material of the charge substantially facilitated, particularly near the ends of the horizontal cristallizer, where an inclined flow direction of the plasma from the nozzle is more advantageous.

DESCRIPTION OF DRAWINGS A plasma kiln according to this invention is shown by way of example in the accompanying drawing, where FIG. 1 is a schematic overall view of the kiln with the fundamental wiring diagram.

FIG. 2 a cross section of a cristallizer with a trough composed of a number of tubes cooled by water and FIG. 3 is a cross section of a cristallizer with a water cooled trough having a mantle composed of a double wall.

DESCRIPTION OF PREFERRED EMBODIMENT The plasma kiln as shown in FIG. 1 comprises an external mantle 3 and an internal mantle 5, which together with the respective covers 7 determine together the internal space of the kiln. Cooling water flows in the space between the external mantle 3 and the internal mantle 5. A cristallizer 1 supported on a supporting tube 4 can be moved within the kiln space within reach of a plasma torch 2. The supporting tube 4 passes through openings in the covers 7 and serves simultaneously for the water supply to the cristallizer l. The gas generated by the disintegration of the plasma is removed from the kiln via an opening in the cover 7. The cristallizer l is moved in direction of its longitudinal axis in a suitable distance from the plasma torch 2 by means of a screw 8 rotated by a motor 10 and by means of a nut 9 provided with take along means, transmitting this movement to the supporting tube 4 of the cristallizer 1. The cristallizer 1 has on both ends face walls 6 cooled by water, which face walls 6 limit the cristallizer 1. There is furthermore an observation means 11 of the plasma kiln, connected to the supply 14 of working gas from a pressure container 15. Th supply 14 of working gas is simultaneously connected to the plasma torch 2. The positive pole of electric direct current is connected to the cristallizer 1 from the current source 13 by a couple of parallel branches of electrical conductors to both ends of the horizontal cristallizer 1. Adjustable resistors 12 are shown in both branches, FIG. 2 shows a cross section of a cristallizer l composed of a number of tubes 16 arranged to the shape of a trough provided on both ends with face walls 6. Cooling water is passing trough all tubes 16. FIG. 3 shows a cross section of a cristallizer comprising a double wall 17 serving for passage of water.

With the plasma kiln according to this invention not only metals with high melting point and of high purity can be remolten, but when using small advance speeds of the cristallizer (of the order of several centimeters per hour) also a zone raftination of metal can be performed by zone melting.

The supply of working gas to the space of the observation means can be also secured by an independent conduit from a pressure vessel or by way of a gas pump.

An axial or inclined flow of the. plasma can be achieved by changing the value of the electric resistors 12 in the parallel supply conductors of the electric current. The control of the direction of the flow of the plasma could be also obtained by selection of different cross sections of both parallel conductors or of the connection place to the supporting tube of the cristallizer with respect to its transverse axis of symmetry.

I claims:

1. Plasma kiln for melting of metals and for forming of ingots comprising in combination:

a vessel defining a kiln space provided with a plasma torch,

a horizontal cristallizer of the shape of a trough adapted to be moved in its longitudinal direction within reach of the effect of the plasma torch,

a source of electric current,

one pole of this source connected to the plasma torch, the other pole by two parallel branches of conductors to both ends of the horizontal cristallizer,

a source of working gas for the plasma torch,

observation means enabling visual control of the melting process,

these observation means connected to the source of working gas, creating an overpressure in these observation means with respect to the kiln space.

2. Plasma kiln as in claim 1, the trough of the cristallizer having double walls defining a space for passage of cooling water.

3. Plasma kiln as in claim 1, the trough of the cristallizer composed of a number of adjacent substantially parallel tubes for passage of cooling water.

4. Plasma kiln as in claim 1, an adjustable resistor arranged in at least one of said parallel branches of conductors connecting the cristallizer with the source of electric current.

* l l i 

1. Plasma kiln for melting of metals and for forming of ingots comprising in combination: a vessel defining a kiln space provided with a plasma torch, a horizontal cristallizer of the shape of a trough adapted to be moved in its longitudinal direction within reach of the effect of the plasma torch, a source of electric current, one pole of this source connected to the plasma torch, the other pole by two parallel branches of conductors to both ends of the horizontal cristallizer, a source of working gas for the plasma torch, observation means enabling visual control of the melting process, these observation means connected to the source of working gas, creating an overpressure in these observation means with respect to the kiln space.
 2. Plasma kiln as in claim 1, the trough of the cristallizer having double walls defining a space for passage of cooling water.
 3. Plasma kiln as in claim 1, the trough of the cristallizer composed of a number of adjacent substantially parallel tubes for passage of cooling water.
 4. Plasma kiln as in claim 1, an adjustable resistor arranged in at least one of said parallel branches of conductors connecting the cristallizer with the source of electric current. 